Polycarbonates from 1, 4-bis-(beta-hydroxyethyl)-benzenes-bis



United States Patent: O

POLYCARBONATES FROM 1,4-BIS-( 3-HYDROXY- ETHYL)-BENZENES-BIS-(ALKYL OR ARYL CAR- BONATES) Delbert D. Reynolds and John Van Den Berghe, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application December 8, 1953, Serial No. 397,037

17 Claims. (Cl. 260 -77.5)

This invention relates to highly polymeric linear polycarbonates prepared by the self-condensation in the presence of an ester-interchange catalyst of a 1,4-bis(B-hydroxyethyl) benzenebis (alkyl or aryl carbonate). These starting materials are hereinafter referred to as bis-(carbonate) monomers. This invention also includes polycarbonates prepared by condensing mixtures of these bis-(carbonate) monomers. Furthermore, this invention relates to the processes involved in preparing the monomers and polymers.

It is an object of this invention to provide unexpectedly and unusually superior highly polymeric linear polycarbonates which are valuable in preparing fibers, film etc. as described herein. It is a further object of this invention to provide l,4-bis-(B-hydroxyethyl)-benzenebis-(alkyl or aryl carbonates) as monomeric starting materials for the preparation of the polycarbonates. An additional object of this invention resides in providing a process for converting the bis-(carbonate) monomer starting materials into the polycarbonates. Other objects will become apparent hereinafter.

Linear polycarbonates prepared by the condensation of p-xylene glycol and m-xylylene glycol with an alkyl carbonate had been described by Carothers and his followers in the prior patented art as well as in Carothers collected papers. Practically no subsequent work appears to have been performed in connection with the preparation of such linear polycarbonates. The materials prepared as described in Carothers collected papers were of relatively low molecular weight and do not constitute highly polymeric linear crystalline polycarbonates which have high melting points, high intrinsic viscosities and which are useful in the formation of photographic film, fibers, threads, textile fabrics, electrical insulating materials, etc. The product obtained by Carothers is said to be a powder melting at less than 185 C. and having a molecular weight of not much more than 1,000. The products of the instant invention are highly polymeric polycarbonates which possess high intrinsic viscosity and high meltingpoints such that they can be extruded to form films and the like which can be mechanically worked and heat-set to form molecularly oriented structures. According to Carothers, all of the polycarbonates described were prepared by alcoholysis between a glycol and ethyl carbonate in the presence of an alkaline catalyst, such as sodium, whereby vapors of an alcohol were driven off by heating. 7

One of Carothers followers suggests that a trace of an aliphatic dibasic acid can be introduced into the reactants in Carothers process whereby super polycarbonates" can be produced by heat under a vacuum.

The prior art does not describe any satisfactory pro cedure which will produce linear highly polymeric polycarbonates having melting points of about 215 C. and

having intrinsic viscosities'of at least about 0.7 in a 60% phenol: 40% tetrachloroethane solution. The process'of the instant invention represents a great improvement over 2,789,970 Patented Apr. 23, 1957 'ice ' properties, etc.

This invention is limited in scope to those particular bis-(carbonate) monomers disclosed since experiments demonstrate that only such compounds and a few others described in copending applications can be employed to produce highly polymeric linear polycarbonates of the type with which this invention is concerned.

The process of this invention for producing the novel polycarbonates comprises (A) self-condensing a bis-(carbonate) monomer having the following formula:

wherein R1 and R2 each represents a radical selected from the group consisting of lower alkyl radicals containing from 1 to 4 carbon atoms and aryl radicals of the benzene series containing from 6 to 8 carbon atoms, (B) in the presence of am ester-interchange catalyst containing titanium as the metallic element, which catalyst can be selected from the group consisting of Ti(OR')4, TiX4 and ether complexes of T iXa. wherein the ether complexes are derived by reacting TiX4 with an ether selected from the group consisting of aliphatic and alicyclic ethers containing from 2 to 12 carbon atoms, and wherein R represents an alkyl radical containing from 1 to 18 carbon atoms and X represents a halogen atom, (C) at an elevated temperature, (D) the condensation being conducted in an inert atmosphere and (E) the latter part of the condensation being conducted at a very low pressure.

It can readily be seen from the description of the process that there is no problem involved in adjusting the ratio of carbonate constituent to l,4-bis(B-hydroxyethyl)- benzene constituents in the reaction vessel since the polycarbonates are produced according to this invention by the self-condensation of only one starting material. This establishes the composition of the polycarbonate produced since there can be no variation in the proportion of carbonate and glycol constituents. Moreover, the nature of this process makes it admirably suited to conducting the process on -a continuous basis since no problems are involved in maintaining critical proportions of reactants.

Examples of the starting materials, i. e. the bis-(carbonate) monomers which can be used in the process of this invention include 1,4-bis-(B-hydroxyethyl)-benzeuebis-(ethyl carbonate), 1,4-bis-(B-hydroxyethyl)-benzenebis-(p-tolyl carbonate), 1,4-bis-(B-hydroxyethyl)-benzene-bis-(phenyl carbonate), 1,4-bis-(fl-hydroxyethyl)- 'benzene-bis-(n-butyl carbonate), 1,4-bis- (B-hydroxyethof titanium can be satisfactorily employed as catalysts to produce thepolyesterspfthis invention. Other compounds, even including some compounds of titanium, which are well recognized ester-interchange catalysts pro a d mote the degradation of the starting material with the formation of ethylenic unsaturation and cross-linking.

This aspect of the invention is discussed in greater detail hereinbelow.

Thetitanium .catalystsdescribed above can be advantageously employed in an amount of fromabout 0.005% to.,about.0.2% by weight basedon the weight of the.bis- (carbonate) monomer being condensed. Higher or lower percentagescan also be employed.

The temperature at which the condensation ,is con- .ducted depends upon whetherthe process is conducted in 11.1 3 Solid phase or in the liquid phase. When either type of process is used, the temperature can be advantageously increased during the course of thecondensation. Ad-

vantageously,rthe reaction can be considered as being conducted in two stages. Thetemperature to which the condensationreaction mixture is initially raised at the be ginning of stage I is advantageously in excess of 200" C. Lower temperatures canalso beemployedalthough :it is generally advantageous to use an initial temperature of, at least about 200 C. Although it is convenient to consider thecondensation process as being conducted in two separate stages, the actual condensation itself continues smoothly fromstage 1 into stage II. The principle .ofdistinction between the so-called two stages lies in the fact that during stage II, the pressure of the adja- -cent atmosphere under which the condensation is .per-

formed is greatly reduced. Although the temperature can remain the same for both the first and the second :stage, it is advantageousto employ a somewhat .higher temperature at about thesame time the pressure is re .duced, especially when the liquid phase processisbeing employed. The temperatures used during the latter part of stage II can advantageously be at least 250 or higher; .the maximum temperature which can be employed is determined by the tendency of the polycarbonate to decompose at extremely high temperatures. As a practicalrnat- "ter, it is most advantageous toemploy a maximum temperature of not much more than about 250 C. Whena solid phase process is employed, .the maximum tempera- ;t ure can be restricted to much lower temperatures, al-

though -the time-.required to accomplish the production ,of desirable linear polymericpolycarbonates may 'be in- ,creased accordingly.

The reduced pressure which is employed during stage ,I-I-ofthe condensation is advantageously less than about mm. of Hgof pressure. Most advantageously, .the pressure is about 0.5 mm. of Hg of pressure. Generally .;Spcaling, pressures are employed which arethe lowest pressures obtainable by the employment of an efficient high-vacuum mechanical pump. Such pressures are, generallyzin the range of less than 1 mm. of Hgpressure.

.The time required for each of the two stages can .advantageously be from about one half to 4 or. 5 hours.

Longer or shorter periods of time can also be employed. 1

,ester 'of carbonic acid willbeevolvedfas, a gas,vas, in'di- .cated hereinabove. Stirring facilitates theremoval of this material in its gaseous form. Either as an aid to the stirring operation or in lieu thereof,,the :inert gasc an beadvantageously bubbled throughthe reaction mixture reby. the removal ,of the carbonic, acidester iszalso .l tats h ev ri u scnditiq d s. h .ds.-sorn wha enerally .rcisab xeinrgsars tolhapmqss iot-this intent on sen 75 a5 obviously be altered to suit the particular starting material being condensed and other conditions which are specific to the reaction being accomplished depending upon the particular set of circumstances. These variations are set forth to some extent in the examples below.

The products of this invention are linear highly polymeric crystalline polycarbonates having melting points of .aboutd2l5'- C.,.%high intrinsic 'v-iscosities and containing the following repeated units:

wherein-the units are"iconnected by ester linkages. In this specification, all intrinsic viscosities are measured by standard procedures employing solutions in phenol 40% sym. tetrac'hlorethane. The melting points of the polycarbonates described in the examples hereinbelow were all at least 210 C. and were generally from 215.-to 225 C.

The bis-(carbonate) monomers of this invention have been found -to-possess certain qualities that can be improved upon by the'formation of interpolycarbonates as described in our copending applications, Serial Numbers 407,804, 407,805, and407,806,"filed on February 2, 1954. Besides employingbis-(carbonate) monomers in the for- -mation of i-nterpolycarbonateathe polycarb-onates of this invention can be mechanically admixed with other polycarbonates to form mixed polymers possessing average properties derived from the various components of the mixture. it is similarly obvious that both the unmodi- -fied polycarbonatesand interpolycarbonates can be suitably blended -or mixed with other polycarbonates, polyxesters, polyurethanes, polyamides, polystyrenes, polyethylene,-etc. insofar as, the polycarbonates of this invention are compatible with-suchhigh polymers. The products vwhich can be produced include W.axes,fibers, molded articles, extrusion -products,'coatin g materials, etc.

The polycarbonates .ofthis-invention can be prepared by :vari-ous continuous processes employing many types of apparatus knowntobe useful in conducting various related continuous-processes as described in the prior art, -fo1':example,=the methoddescribed in U. S. 2,647,885 can besuitably adapted. For another example, reference a .is made to application, Serial No. 397,040 filed on even date herewith.

Thezbis-(carbonate) monomers employed in accordancewwithlhisinvention can'be prepared by condensing an alkyl or'anv aryl chlorocarbonate with 1,4-bis-(,8-hycdroxyethyll benzene inqthe presence of pyridine. Al-

though it is. advantageous :tocarry out this condensation in a-ztertiary,arninev such .as pyridine, other acid-binding agents can alsobe employed. ,Advantageously, the reaction mixturecanbe'cooled to prevent excessive increase in.-temperature. ;-Advantageously, more than two mole proportions-mfalkyl or-aryl'chlorocarbonate or brornovfiflrbonatc .areemployed for each mole proportion of Abis-(fihydroxyethyl)rbenzene. Upon suitable purificavtion,.the .reactiommixture;gives a good yield of a 1,4-bis- .(fi-hydroxyoth-yl)-benzcnerbis-(alkyl or aryl carbonate). -Various modifications of thisuprocess can obviously be .employedto produce thevarious bis-(carbonate) mono- -.mersta-rting rnaterials.

The following-example will serve to further illustrate how these bis-( rbonate) .monomers can be prepared:

PREPARATIONQF 1 ,4- BIS- (-EHYDROXYETHYL B ENZENEBIS (ETHYL CARE GNATE) A. 141,064)icarbethoxy-p-xylene.+Two kg. of sodium cyanide wasdissolved in-3 liters of Water contained in 22 l. .fiask. Eightyliters ethyl alcohol was added, the mixture was stirredandheated in :astem bath to -80 C. With jthafitram .911, '2,akg.:pfpnylyleneehloride was added as fast ;a their-ratetpf reaetipnpermitted 6 15120 min). About vimltes afterithealast. of: the .chloride was added, the

flask was, filled with-cold water, andafter-cooling-to" about 20 the product was separated by filtrationand air dried. The air dried product was recrystallized from about l2 l. of alcohol. An insoluble portion'(65-g.) is obtained. The yield of p-xylylene dinitrile was 1440 g.

(80%), M. P. 92-95 C. After one more crystallization, the M. P. is 96-97 C. Twelve hundred grams of the p-xylylene dinitrile was dissolved in a mixture of 12 l. anhydrous benzene and 3 l. of absolute ethanol. The mixture was stirred at 20-35 C. While anhydrous HCl was passed in for 7 hours. The reaction mixture was allowed to stand over night (16 hours), then filtered by suction, washed with ether and dried. The yield of the iminoester hydrochloride was 2 kg. (81%).

The iminoester hydrochloride (2 kg.) was stirred for two-hours at about 80 C. with four times its weight of boiling water. It was their filtered and crystallized from alcohol. Yield, 1210 g. (78%); M. P. 56-58".

B. 1,4-bis-(ti-hydroxyethyl)-benzene.-To a slurry of 48 g. 1.25 moles) of powdered lithium aluminum hydride in- 400 m'l.of -anh'ydrous ether was added with vigorous stirring at a rate to maintain a rapid reflux of the'ether a solution of 250 g. (1 mole) of a,ot'-dicarbethoxy-p-xylene' in 2 l. of anhydrous ether. The addition required one hour. Refluxing was continued on a steam bath' for two hours after which the mixture was cooled and 88 ml. (5 moles) of water was cautiously added. Stirring was continued for two hours and the mixture was filtered. Evaporation of the ethanol filtrate and multiple extractions of the precipitated salts with hot benzene followed by removal of the benzene in vacuo gave 152 g. (91%) of 1,4-bis-(B-hydroxyethyl)-benzene, M. P. 87-88.

C. 1,4-bis-(fi-hydroxyethyl)-benzene-bis-(ethyl carbonate).-One kilogram (6 moles) of 1,4-bis-(5-hydroxyethyl)-benzene was dissolved in 2 l. of pyridine and the solution cooled to 5. The solution was stirred and 1426 g. (13.2 moles, 1256 ml.) of ethyl chlorocarbonate was added at such a rate that the temperature of the mixture did not exceed 20. The addition required 2.5 hours and the mixture was stirred for an additional two hours. After standing overnight, the mixture was poured, with vigorous stirring, into ice/and water. The precipitated product was filtered cold "and recrystallized by dissolving it in ethyl alcohol at 40-45 and cooling the solution to -20.. The pure white product amounted to 1525 g. (82%); M. P. 37-38.

D. 1,4-bis-(fl-hydroxyethyl)-bis-(phenyl carbonate).- The procedure described above was repeated except that phenyl chlorocarbonate was employed in lieu of the ethyl chlorocarbonate.

L E. 1,4-bis-(B-hydroxyethyl)-benzene-bis-(pentyl. carbonate).The procedure described above was repeated except that pentyl bromocarbonate was employed.

' It is believed readily apparent that other corresponding bis-carbonate monomers can be prepared employing alkyl or aryl chlorocarbonates wherein the alkyl radicals contain from 1 to 8 carbon atoms and the aryl radicals are members of the benzene. series. containing from 6 to 8 carbon atoms. W

' The bis-(carbonate) monomers, prepared as described above, can be employed in accordance with the following examples which serve to further illustrate this invention as regards the polycarbonates and their preparation:

4 Example. 1 .:'-P0lycarb0nate employing. titanium batoxia'e as catalyst rapidity to give a white porcelain-like product; M.

215" C.; viscosity 0.87. 7

Example Z P-Polycarbonate employing titanium butoxide as catalyst Two hundred grams of 1,4-bis-(fi-hydroxyethyl)-ben zene-bis-(phenyl carbonate) was melted, and eleven drops of titanium butoxide was added. The reaction mixture was heated under an atmosphere of nitrogen for an hour and twenty minutes in an oil bath at ZOO-240 C. (stage I). formed was distilled from the reaction flask. The reaction mass was then stirred at 0.5 mm. Hg pressure for three hours and forty minutes while being heated in a 255 C. oil bath (stage II). Upon cooling, a white crystalline porcelain-like product was obtained. The intrinsic VlS-,' cosity as measured in a 60:40 phenol: tetrachloroethane;

mixture was 0.78; M. P. 215 C.

Example 3.Palycarbonate empolying titanium butoxide as catalyst Fifty grams of 1,4-bis-(fi-hydroxyethyl)-benzene-bis- (ethyl carbonate) containing two drops of titanium but-' oxide was heated for two hours, under nitrogen at 250 C.'- A vacuum-- pump was attached, the temperature raised to 260 C.' and the reaction mixture stirred at 0.3 mm. of Hg for The ethyl carbonate was allowed to distill.

minutes. Upon cooling, the product crystallized to a white, hard porcelain-like product. The intrinsic viscosity in a 60:40 phenohsym. tetrachloroethane mixture was 0.81. The melting point was 215 C.

Example 4.P0lycarb0nate employing titanium bntoxide as catalyst A quantity of l,4-bis-( 8-hydroxyethyl)-benzene-bis- (ethyl carbonate) and Ti(OC2H5)4 as the catalyst treated as above. The temperature for stage I 220 C.;

for stage II 250 C. Time for stage I, 1 hour and 40- minutes; for stage II, 1 hour and 50 minutes. During stage II, the pressure was 0.9 mm. of Hg. The product was crystalline and white in color.

Example 5.P0lycarb0nate employing titanium buto xide as catalyst ,Two hundred grams of 1,4-bis-(p-hydroxyethyl)-benzene bis-(butyl carbonate) was placed in a 500 cc. flask equipped with a ground glass neck and a side arm. Ten drops of titanium butoxide wasadded and the reaction mixture was melted in a 250 C. oil bath. Hydrogen was bubbledthrough the reaction mixture during'stage I. Dibutyl carbonate was removed by distillation. After one hour and forty minutes, a stirrer assembly was in serted, and the reaction mixture stirred under 0.4 mm..

pressure for 3.75 hours and forty minutes. The result- .ing polymer crystallized rapidly when cooled. It was a. hard, white porcelain-like product with an intrinsic vis-. The viscosity was measured in a 60:40'

cosity of 0.83. phonolztetrachloroethane mixture.

The catalysts employed in accordance with the instant invention result "in the production of polycarbonates' which have .the advantageous properties described hereinabove whereas many of the other better known esterinterchange catalysts result in the production of polycar-- produce unsaturation within the molecule whereby 016*- During this period, the phenyl carbonate which was greases fiiiiocharactersuch as in" styrene" is created. A's-"a 're sult, the polymers produced are not linear-in structure, but

are cross-linkedand of novaluefor fibers, film etc. .where molecular orientation is desired.

It would appear that the structure existing in the bis- (carbonate) monomer is unstable and decomposes in the presence of most ester-interchange catalyststo yield vari ous undesirable products.

This situation demonstrates the unusual advantagesof employing the titanium catalysts covered by the applicants invention. Several of the preceding examples illustrate the employment of titanium butoxide as the catalyst. This compound and many of its' homologs are thick liquids.- about 0.0002 equivalent of titanium. It is sometimes advantageous to dissolve these liquidsin an alcohol to facilitate'handling the catalyst;

Another titanium compound-which has-been found to be useful is titanium tetrachloride. Titanium tetrachloride is 'difiicult to handle because of. its rapid reaction with the moisture in the air. It has therefore been found advantageous to employ thisicompound in the form of an ether complexnln preparingthesecomplexes, the lower aliphatic ethers containing from .2 to 8 carbon atoms on either side of the central oxygen: atom and thecyclic ethers such as 1,4 dioxane can be employed The ether complexes are prepared advantageouslyv by adding titanium tetrachloride slowly to an excess of the ether. vantageous to maintain the ether at ambient temperatures (2030 C.) or lower during this addition. Examples regarding the preparation of these ether complexes-are presented as follows:

Example 6.-1,4-dixane complex with TiCl4 Titanium tetrachloride was added slowly to an excess of 1,4-dioxane. Theyellow prec'ipitate which formed was filtered and. dried-in a vacuum desiccator over P205. Assuch, it would be conveniently used as a catalyst.

Example 7.Diethyl ether complex of TiCls Example 8.-Polycarb0nate employing diethyl ether complex of TiCl4 as catalyst A tenz-gram. sample of 1,4-bis-(5-hydroxyethyl) benzene-bis-(ethyl carbonate) was heated under nitrogen with 0.1 gm. of'the ether complex (Example 7) for twenty-five minutes at 250 C. The catalyst dissolved immediately and. diethyl carbonate began to distill Within about three minutes. After the initial twenty-five minute stage, thezreaction mixture was stirred under vacuum for one hour and forty-five minutes (stage II). The product was similar to that described in Example 9.

Example 9.P0lycarb0nate empl0ying TiCl4 as catalyst Fifty grams of 1,4-bis-(flhydroxyethyl)-benzene-bis- (ethyl carbonate) was heated with six drops of titanium tetrachloride, under nitrogen, for one hour in an oil bath maintained at250 C. The resulting product was then stirredlunder- 0.2- mm. pressure for an additional 2.25

hours. at250 C.' The're'sulting'clear; viscous melt crys'-'- tallized'rapidly upon cooling to yield a dense; hard; white porcelain-like product. It was soluble in 60:40 phenol: tetrachloroethane at 110 C. and had an intrinsic viscosityof 0.77.

Example 10I-P0lycarbonate employing TiBm as catalyst.

The :process described in. Example 8 v'va'srepeatedex actly except that: TlBM was employed as the catalystt v One drop weighs about 0.015gram and contains It is ad 8 'Ihe-polymerobtained was'e'ssentiallyfthe same as in Ex ample 8; it had'a'melting point'of 215 C;

Example '11 .Po'lycarbonate"'employ'iizg Ti(OC 11H2 s) 4 as catalyst-' The process described in Example 3 was repeated exactly except that Ti(OC11H2s)4 was employed as the catalyst. The polymer obtained was essentially the same as in Example 3 except for a melting point-of 220- C.

It is believed that the preceding examplesmake it clearly apparent that the specified titanium catalysts are essential to the'preparationoflinearhighlypolymeric crystalline polycarbonates when self-condensing the bis- (carbonate) monomers of this invention. Othercatalysts such as the alkali metal and the alkaline earth metalalkoxides are strikingly inferior to thesetitanium compounds.

The polycarbonates of this invention can be prepared employing other catalysts-and other reaction conditions in a manner analogous to that described in the preceding examples. within the scope of-the ranges and limitsset forth hereinbefore.

The polymeric products embodying this invention can be prepared either batch-wise or continuously, and can be used along or in admixture with similar or-dissimilar polymeric materials and with or without the usual modifiers or compounding agents for polymeric materials. Materials embodying the invention can be used for forming fibers, for extrusion orv molding applications, or for film or sheet applications such as for film supports for black and white or color photographic films.

The photographic films which can be produced can advantageously comprise a film support of the abovedescribed polycarbonates upon which is deposited one or more layers of a silver halide emulsion which can contain appropriate sensitizers or other additives to suit the intended photographic use.

We claim:

it. A process for preparing a highly polymeric linear polycarbonate comprising (A). self-condensing a bis- (oarbonate) monomer having the following formula:

wherein R1 and R2 each represents'a radical selected from the group consisting of lower alkyl radicals containing from 1 to 4 carbon atoms and aryl radicals of the benzenc series containing from 6 to 8 carbon atoms, (B) in the presence of an ester-interchange catalyst containing titanium as the metallic element, which catalyst is selected from the group consisting of Ti(OR')4, TiX4 and ether complexes of TIX4 wherein the ether complexes are derived by reacting T iX4 with an ether selected from the group consisting of aliphatic and alicyclic ethers containing from. 2 to 12 carbon atoms, and wherein'R represents an alkyl radical containing from 1 to 18 carbon atoms and X represents a halogen atom, (C) at an elevated tempera ture, (D) the condensation being conducted in an inert atmosphere and (E) the latter part of the condensation being conducted ata very low pressure.

2. A process as defined-in claim 1 wherein the elevated temperature during the course of the condensation is in excess of about 200 C.

3. A process as defined-in claim 2 'wherein-theesterinterchange catalyst is employed inuan amount of from about 0.005% to about 0.2% based on the weight of the weight of the bis (carbonate) monomer.

4. A process as defined in claim 3 wherein the low pressure is less than about 15 mm. of Hg pressure.

5. A process as defined in claim 4'wherein the bias (carbonate) monomer is. 1,4-bis-(,B-hydroxyethyU-ben zene-bisethyl carbonate) 6. A linear highly polymeric: polycarbonate having a melting point above about 215 C. which is composed of the following repeating units:

wherein the units are connected by ester linkages and one end of each polymer molecule contains and Ri-radical attached to the terminal free oxygen bond and the other end of each polymer molecule contains an radical attached to the terminal free methylene bond, wherein R1 and R2 each represents a radical selected from the group consisting of lower alkyl radicals containing from 1 to 4 carbon atoms and aryl radicals of the henzene series containing from 6 to 8 carbon atoms.

7. 1,4-bis-(B-hydroxyethyl)-benzene-bis-(ethyl carbonate).

8. A process as defined in claim 3 wherein the catalyst is titanium butoxide.

9. A process as defined in claim 3 wherein the catalyst is the diethyl ether complex of titanium tetrachloride.

10. A process as defined in claim 3 wherein the catalyst is titanium tetrachloride.

11. A process defined in claim 3 wherein the catalyst is the 1,4-dioxane complex of titanium tetrachloride.

12. A process as defined in claim 3 wherein the catalyst is titanium tetrabromide.

13. A compound having the following formula:

wherein R1 and R2 each represents a radical selected from the group consisting of lower alkyl radicals containing from 1 to 4 carbon ato-ms and aryl radicals of the benzene series containing from 6 to 8 carbon atoms.

14. 1,4 bis (B hydroxyethyl) benzene bis (isopropyl carbonate).

l5. 1,4-bis-(5-hydroxyethyl)-benzene-bis-(phenyl carbonate).

16. 1,4 bis (18 hydroxyethyl) benzene bis (butyl carbonate).

17. 1,4 bis (B hydroxyethyl) benzene bis- (pentyl carbonate).

References Cited in the file of this patent UNITED STATES PATENTS 2,210,817 Peterson Aug. 6, 1940 2,379,252 Muskat June 26, 1945 FOREIGN PATENTS 879,250 France Nov. 10, 1942 OTHER REFERENCES Carothers Collected Papers, High Polymers, vol. I, Interscience, New York (1940), pages 31 and 41. 

1. A PROCESS FOR PREPARING A HIGHLY POLYMERIC LINEAR POLYCARBONATE COMPRISING (A) SELF-CONDENSING A BIS(CARBONATE) MONOMER HAVING TH E FOLLOWING FORMULA: 